I don't think we'll need to worry about the reasoning in the end of it; Marvel isn't exactly shying away from referencing the events of the Avengers, seeing as Tony is having a difficult time with it since.

"Nothing's been the same since New York."

I'm sure we'll get a reason as to why Tony can't call for backup.

Feige has said it will be shown/discussed why SHIELD and the other Avengers can't help Tony out in his situation. The Mandarin is probably going to poison everyone against Tony, making him a criminal and a pariah that nobody wants to associate with.